Halogenated copolymers of isobutylene and up to about 4 mole % of isoprene (butyl rubber) are well known polymeric materials whose vulcanizates offer some outstanding properties not possessed by many other diolefin based elastomers. Articles prepared from many cured halogenated elastomers offer improved resistance to oils and greases as well as resistance to oxygen and ozone degradation. Butyl rubber vulcanizates exhibit good abrasion resistance, excellent impermeability to air, water vapor, and many organic solvents, as well as resistance to aging and sunlight. These properties render these materials ideal candidates for one or more applications such as water hoses, organic fluid hoses, components in tire construction, gaskets, adhesive compositions and various molded articles.
More recently, new halogenated elastomeric interpolymers have been discovered which offer many of the same properties as halogenated butyl rubber, but are even more ozone and solvent resistant and are more readily curable. These materials are the halogenation product of random copolymers of a C.sub.4 to C.sub.7 isoolefin, such as isobutylene, and a para-alkyl styrene comonomer wherein at least some of the alkyl substituent groups present in the styrene monomer units contain halogen.
These copolymers and their method of preparation are more particularly disclosed in U. S. Pat. No. 5,162,445, the complete disclosure of which is incorporated herein by reference.
The aromatic halomethyl groups present in such copolymers permit facile crosslinking to be accomplished in a variety of ways, including by means of zinc oxide or promoted zinc oxide curing systems normally used to cure halogenated butyl rubber.
Some of these promoted zinc oxide crosslinking systems, however, give serious precure problems.
U. S. Pat. No. 5,373,062 discloses halogenated elastomer compositions featuring a promoted zinc oxide crosslinking agent and a bismuth carboxylate scorch inhibitor.
It is an object of this invention to provide halogenated elastomer compositions which cure quickly, but without serious precure problems, and achieve a high level of crosslinking.